I installed Oracle Instant Client 11.2 on a desktop with Win 7. Then I created a System DSN using MS ODBC Data Source Administrator (selected the Instant Client driver). The TNS Service Name is set to one of our databases on a separate server.

1) Instead of having the tnsnames.ora file reside on the desktop. Is it possible to configure Instant Client to use a tnsnames.ora file on a different server? I'm trying have it so that when I create the System DSN, the TNS Service Name drop down box displays all the aliases listed in the remote server's tnsnames.ora file. Is this possible?

I tried creating a new environment variable on the desktop named TNS_ADMIN. Setting the value to a mapped drive that I created. The map drive points to the directory location of the remote servers tnsnames.ora file (O:\network\admin).

If you want to avoid having to customize tnsnames.ora files on every client and use a centralized approach instead,
you should use "directory naming".
See http://docs.oracle.com/cd/E11882_01/network.112/e10836/concepts.htm#sthref144

While using a tnsnames.ora file on a CIFS share is not something I would do for a production system,
it should work. What problems do you encounter?

While in ODBC Data Source Administrator. When I attempt to create a new System DSN using the Oracle in instantclient_11_2 driver. The test connection fails with the following error: Unaable to connect SQLState=08004 [Oracle][ODBC][Ora]ORA-12154: TNS:could not resolve the connect identifier specified.